1. Field of the Invention
This invention generally relates to an offset, rotary, printing press and, particularly, to such a press with a spray bar assembly for spraying dampening liquid onto a roller.
2. Description of the related art including information disclosed under 37 CFR 1.97-1.99
It is well known in high speed offset printing presses to add dampening liquid to the printing plate mounted on a plate cylinder by means of a train of dampening liquid rollers. The train of rollers includes a dampener roller upon which dampening liquid is sprayed from an elongate spray bar assembly. The elongate spray bar assembly has a plurality of solenoid controlled nozzles spaced along the length of an elongate, generally U-shaped open housing which collectively spray dampening liquid along the length of the roller body.
It is also known to provide a pair of stop plates at opposite ends of the open housing to deflect liquid spraying diagonally from the end nozzles onto the edge of the dampening roller which would otherwise spray beyond the edge. The increased dampening liquid at the edge of the dampener roller resulting from the deflection helps remove ink scumming at the edges of the dampening rollers.
Disadvantageously, optimal spray density to reduce edge scumming is obtained in those known presses only when the width of the paper web, or width of the printing plate, corresponds to the fixed location of the stop plate. When a relatively smaller printing plate is employed, a different spray pattern is required, but in the known printing press it was not possible to adjust the mounting location of the stop plate to obtain different spray patterns or to make any adjustment whatsoever to the spray pattern during operation of the press.
Since it is not possible to make adjustments to the spray during operation, it is not possible to empirically determine the optimum spray setting by making adjustments to the spray pattern during operation for different sized printing plates and webs.